The series from Oxford University Press, Pocket Guides to Social Work Research Methods, has a number of helpful titles on specific aspects of social work research (e.g., clinical data-mining, cross-cultural research, needs assessment, etc.)

Sage Research Methods

Sage Research Methods searches across a large body of the social and behavioral sciences literature from Sage Publications on topics such as designing research projects, understanding methods or identifying new methods, conducting research, and writing up findings.